The invention relates to a sensor arrangement for a vacuum brake booster for determining the pressure conditions prevailing in such a brake booster and a vacuum brake booster provided with a sensor arrangement of this kind.
Information on the pressure conditions prevailing in a vacuum brake booster can be used in various ways. For example, the maximum output operating state of the brake booster, i.e. the state as from which the brake booster is no longer able to assist a further pressure increase, can be detected by sensing the pressure states in the brake booster. Furthermore, sensing of the level of the vacuum in a vacuum chamber of the brake booster may serve, for example, to control a vacuum pump creating the vacuum.
It is of particular advantage to sense the pressure states in a brake booster which is provided with an electromagnetic actuating unit. An electromagnetic actuating unit of this kind enables the vehicle brake system to be actuated by activating the brake booster in addition or as an alternative to pedal force-proportional actuation by the driver. For example, the above-mentioned electromagnetic actuating unit affords the possibility of operating the brake booster at maximum output independently of the pedal actuating force applied by the driver in a critical driving situation, e.g. when emergency braking, and thus providing the maximum possible braking force assistance (so-called brake assistant function). The pressure build-up speed in the working chamber of a brake booster can be used to recognize when a braking action is an emergency braking action. Knowledge of the pressure conditions in the brake booster is also of advantage when braking takes place completely automatically, for example in co-operation with a distance control system.
DE 44 36 297 A1, and corresponding U.S. Pat. No. 5,711,204 which is incorporated by reference herein, discloses a vacuum brake booster in which a pressure sensor is rigidly connected to a moveable wall disposed between a vacuum chamber and a working chamber. The pressure in the vacuum chamber is measured by a second pressure sensor, which is disposed either outside of a brake booster housing or inside the vacuum chamber.
U.S. Pat. No. 4,633,757, which is incorporated by reference herein, discloses a vacuum brake booster with a pressure sensor disposed in a working chamber and a pressure sensor disposed in a vacuum chamber, wherein the pressure sensors are each secured to an inner wall of the brake booster housing. The disadvantage of these known arrangements lies in the fact that assembly and inspection and any necessary replacement of the pressure sensors give rise to significant difficulties and entail considerable expenditure.
DE 197 29 158 C1, which is incorporated by reference herein, describes a vacuum brake booster with a pressure sensor which is disposed in a housing that is externally flange-mounted on a brake booster housing. The pressure sensor is connected to at least one working chamber and at least one vacuum chamber via air guide ducts, which extend from the housing of the sensor arrangement into the brake booster housing. A solution of this kind requires a complex system of air guide ducts. Moreover, the space requirements are increased as a result of disposing the pressure sensor outside of the brake booster housing.